The present invention relates to an optical pickup device and an optical disc apparatus, for recording/reproducing information onto/from an information recording medium having plural numbers of information recording surfaces.
As the background art is already known, for example, Japanese Patent Laying-Open No. 2005-203090 (Patent Document 1). In that publication, as a problem(s) to be dissolved, there is a description, “It is to provided an optical pickup for enabling to restrain coherent light because of a neighboring layer, when recording and/or reproducing a multi-layer disc having plural numbers of recording layers on one side surface thereof, and thereby improving a jitter of a tracking error signal, which is detected by a DPP (Differential-Push-Pull).”, and also is made a description, as a dissolving means, “It has an optical member for restraining the coherent light because of the neighboring layer from being received by a photo detector, when applying to an optical information reservation medium having plural numbers of recording layers on one surface. With this, it is possible to restrain the coherent light because of the neighboring layer from being received by the photo detector, in particular, first and second sub-photo detectors of the photo detector.”
Also, for example, in Non-Patent Document 1 is descried, as the problem to be dissolved, “When recording/reproducing a 2-layer disc, an offset is generated in a TE signal if another-layer stray light, including a light reflecting on a layer differing from a target layer, enters into a photo detector. For this reason, within the conventional structure without a countermeasure against the another-layer stray light, the offset of the TE signal on the 2-layer disc comes to be large, comparing to that in case of a single layer, and therefore a stable control is disturbed.”, and also, as the dissolving means is mentioned, “The photo detector for use of tracking is disposed in a region where no another-layer stray light enters.” And, the structures for that are also described in Japanese Patent Laying-Open NO. 2004-281026 (Patent Document 2).
Also, in the abstract of Japanese Patent Laying-Open No. 2009-170060 (Patent Document 3), as an object thereof, i.e., “to provide an optical pickup device for enabling to obtain a stable servo signal, without receiving ill influences of the stray light from other layer(s), as well as, a focus error signal and a tracking error signal, when recording/reproducing the multi-layer disc”, it is described that “A reflection light from the multi-layer disc is divided into a plural number of regions, wherein a light flux divided forms a focus at a different position on the photo detector, and at the same time, the focus error signal is detected through a knife-edge method with using a plural number of light fluxes; thereby detecting the tracking error signal with using the plural numbers of light fluxes divided. Further, when the focus is fit to the target layer, a divided region and a light receiving surface are disposed, so that no stray light from other layer(s) enters into a light receiving surface for use of the servo signal of the photo detector.”